The present invention is directed to safety syringes, and particularly syringes with retractable needles configured to retract after use and prevent re-use and unintended sticking. Retractable syringes are known in the art, which typically include a needle configured to automatically retract into a syringe barrel after delivery of a medicant into a patient. In some designs, a needle stem including a separable or breakable retaining ring thereabout is installed through a barrel proximal end and secured in the barrel distal end. The needle stem may be fixedly secured or selectively secured to a needle. Conventional mechanisms that secure the needle stem and retaining ring in place define a required axial plunger force required to selectively break the needle stem from the retaining ring after final use to allow automatic retraction of the spring biased needle.
There is desired a retractable syringe configured to enable the retaining ring to break from the needle stem with a reduced plunger engagement force, which provides an improved tactile feeling of the syringe plunger and comfort of use. There is also desired a retractable syringe configured to make it easier to install the needle stem and retaining ring in the barrel distal end, such that it can snap into place therepast with less axial force.